Explaining darker deep convective clouds over the western Pacific than over tropical continental convective regions

Abstract. This study attempted to explain why deep convective clouds (DCCs) over the western Pacific are generally darker than those found over tropical African and South American land regions. The western Pacific domain was further divided into its land and ocean regions to deduce the general differences in DCC characteristics between convectively active tropical land and ocean regions. DCC in this study is defined as a single-layer cloud whose thickness is greater than 15 km, and it is determined from CloudSat-measured reflectivity profiles. Corresponding MODIS-measured reflectivities at 0.645 μm were examined, along with the analysis of cloud products from Cloud Aerosol Lidar Infrared Pathfinder Satellite Observation (CALIPSO) measurements.

From an analysis of the four January months of 2007–2010, a distinct difference in ice water path (IWP) between the ocean region of the western Pacific and the three tropical land regions was revealed. Distinct differences in the effective radius between land and ocean were also found. The findings lead to a conclusion that smaller IWP over the western Pacific ocean region than over the tropical land regions, which should be caused by different cloud microphysics between land and ocean, is the main cause of smaller reflectivity there.